Hopefully you can use the so called 1/4" Lexan which actually measures approx .200" or 5mm thickness. It's much stronger and flexes so much less than the so called 1/8" which measures approx .100" thickness. Your TC front window gets the full force of the oncomming buffeting winds when driving. Constant flexing of the thinner Lexan will tend to open joints and seals and seep/wick water in.
I have always made my own storm windows for inside our RV's and some of the windows in our homes since the 1990's and use only the 1/4". The storms on our homes are mounted on the inside and have an annodized aluminum "C" window frame channel around the outside with rubber seals. Looks professional and work great. Ever try to lift a 4' X 8' thick glass plate storm window to put it on the inside of a big picture window? 2 weight lifters and an elephant comes to mind and the darn elephant will likely leave a few piles on the carpet! The Lexan storm on the big Thermopane picture window made night and day difference for cold transfer and also eliminated sweating in winter. Stopped the cold air drafts going down off the huge window. Also had replaced a broken side window with Lexan on our daughter's RV and you can't tell it from glass even 7 years later.
Yes, weight is a factor and even more so in RV's. Yes, it can or will scratch but it's easy and cheap to replace if it gets too bad after a long time.
